Co-pending application Ser. No. 892,271 entitled "POROUS HIGHLY EXPANDED FLUOROPOLYMERS AND PROCESS THEREFOR", incorporated herein by reference, discloses the use of elastomers which strengthen expanded poly(tetrafluoroethylene) fibrils by forming a continuous matrix interpenetrating the microstructure of the fibrils. In so doing, it renders the poly(tetrafluoroethylene) structure porous but yet durable with excellent pliability for use as a vascular graft. More importantly, however, addition of an elastomer to the poly(tetrafluoroethylene) allows an implant or preferably, a vascular graft made from the material to be biologically compatible with surrounding tissue.
This invention relates to a multi-layered polytetrafluoroethylene/elastomer material that can be formed into an implant where there is an improvement in the luminal hydrophobicity, suturability, compliance, strength and elasticity due to the novel arrangement of respective layers of poly(tetrafluoroethylene), polytetrafluoroethylene/elastomer and elastomer. This invention relates to materials utilized in the production of devices for in vivo implantation, such as heart valve leaflets, sutures, vascular access devices or any related products, but more particularly relates to vascular grafts.
Conventional vascular grafts manufactured from porous poly(tetrafluoroethylene) have limitations in their strength and compliance. The porous grafts do not hold or resist dilation unless wrapped with a reinforcing film for support. This reinforcement slows down the tissue ingrowth preventing rapid healing. This is because of the relatively low radial tensile strength of poly(tetrafluoroethylene). In addition, the grafts are stiff and non-compliant to the natural artery.
Prior art patents disclose vascular grafts with laminated materials which are bonded in a manner to place porous, compacted poly(tetrafluoroethylene) in a position to be in contact with the blood surrounded by a layer of a suitable biocompatible material so that the implant allegedly may be accepted by the surrounding tissue. U.S. Pat. No. 4,576,608 describes a vascular graft having two layers, an inner layer comprising a blend of poly(tetrafluoroethylene) fibers and resin having a specific porosity wherein the outer layer comprises a fused blend of poly(tetrafluoroethylene) fibers and carbon fibers or silicone rubber. Other suitable biocompatible materials used in the lamination may be Teflon FEP, manufactured by DuPont Company or other biocompatible fabrics such as polyamide, polyaramid, polyimide or polyester fabric. U.S. Pat. No. 4,321,711 discloses a vascular prosthesis comprising porous tubing of poly(tetrafluoroethylene) containing an anti-coagulant substance and bonded to its outside surface, a porous elastomer coating containing a substance which counteracts the anti-coagulant. Typically, the anti-coagulant substance is heparin. Any heparin antagonist such as protamine may be used in the elastomer coating to counteract the heparin. The elastomer is typically fluorine rubber, silicone rubber, etc. While prior art implants may be porous and flexible, they do not provide the strength, elasticity or biological compatibility of the natural artery. There is a need for an in vivo implantable material that can be formed into a vascular graft which mimics the natural artery composition of collagen and elastin and is acceptable to the surrounding tissue.